Piston Slap: The B7's Bemoaning Fuel Pump?

Sajeev Mehta
by Sajeev Mehta
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piston slap the b7 s bemoaning fuel pump

Paul writes:

Hi Sajeev, I have an opinion/advice question for your column:

I have an ’05 Audi S4 (B7 generation), and this is not a question about this model’s notorious timing chain that so frequently scandalizes car website comment sections.* I have a longstanding issue with fuel pump vibration. It is extremely noisy when it primes, making a rapid clicking or clunking noise that is audible both inside and outside the car. It only lasts for the priming process, and afterwards, the car starts and runs as normal. There is no hesitation in starting, misfiring, or power loss. It is only a noise.

I assumed it was the fuel pump, so I replaced it, but the problem did not go away. I took it to a German car specialist that I’ve used for many years, someone trusted but also somewhat expensive. He confirmed that the pump is not at fault, but suspects that the housing for the pump — which is built into the fuel tank — is broken. There is some kind of vibration dampener assembly that not doing its job and the noise is from the pump rattling the housing around during priming.

Repairing this, according to him, would involve replacement of the entire fuel tank.

This is obviously not a cheap part, and the tank straddles the driveshaft and rear differential, so replacing it would involve dropping both components and that’s beyond my ability to DIY with the tools I have at my disposal. So it would be a very expensive job at a mechanic. Accordingly, I’ve left the problem unfixed for quite some time now.

Should I suck it up and get this fixed? Aside from being unsightly and annoying, it doesn’t seem to be affecting the running of the car. On the other hand, there’s always the possibility that I may be damaging the pump or the fuel tank and setting myself up for an even bigger expense down the road.

Have you ever heard of anything similar to this? I couldn’t find a whole lot online about other B6/B7 owners with this problem. It seems to be a completely aberrant failure and I was thought maybe you had some insight.

* The timing chain problem on these models is completely overblown and can easily be avoided by making sure you change your oil on schedule and maintain the check valves and oil spray nozzle in the heads. The chain slap comes from oil draining out of the heads while the car is parked, slackening the hydraulic chain tensioners until the engine restarts and builds the pressure back up. Audi was smart enough to foresee this issue and build in a pair of check valves designed to maintain oil pressure in the heads while the car was off, but they can fail and stick open over time. Replacing them proactively will keep your chain properly tensioned and avoid the slap issue. I did mine as soon as I started to hear startup noise 25k miles ago and it went away immediately and never returned. Spread the word!

Sajeev answers:

Consider the word spread on the timing chain problem, now get people changing oil at recommended intervals, LOLZ!

Regarding your fuel pump vibration problem, I have an old Fox-body Ford that had a terribly loud aftermarket fuel pump after a terrible conversion from wussy Central-EFI to manly 4-bbl carburetion. The solution was to either to add an isolating rubber bushing/gasket between the pump and the frame (and pray that was enough), or run an old-school mechanical fuel pump off the front of the engine.

But I digress, your Audi has an easy access port under the back seat to eyeball the vibration problem yourself.

I also doubt your vibration damages the fuel tank, and there’s likely a DIY solution. Sharpen your knives, Best and Brightest, I smell a wrong answer forthcoming.

Remove the back seat/fuel pump cover, get a mechanic’s stethoscope, and have someone key-on the car to trigger the fuel pump. After reading this thread, I reckon you’ll isolate the noise quickly without removing anything, and hopefully silence the noise with a GENTLE push or pull on the fuel pump top or the retaining trim ring. If so, you know the source of the vibration may lie elsewhere but can be silenced at the point of contact.

See the rubber ring with the little nubs at each end? I bet that’s the place that needs extra silencing initiatives.

And yes, any tech that values their reputation will replace the whole tank, as I only see proper replacements for that big orange gasket (above). Armchair quarterbacking this problem is a bad move, so my notions involving a thin bead of silicone are going out the window. It really depends on the vibration’s location, how the fuel pump (top part) sits inside the recess, how the locking ring operates, etc.

But I will have faith that this is a cheap fix after some NVH diagnostics on your part.

[Images: Shutterstock user Richard Peterson]

Sajeev Mehta
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  • SCE to AUX SCE to AUX on Dec 23, 2017

    I think Audi could have complexified that design a little more, just to bring it up to proper 'German Engineering' standards. Sheesh. Here's the obvious: This sort of thing doesn't happen on 'cheap' Korean cars. But I guess the Audi experience is worth it for some folks.

  • Sector 5 Sector 5 on Dec 23, 2017

    If this was an EV you wouldn't have this problem.

    • See 2 previous
    • DownUnder2014 DownUnder2014 on Dec 26, 2017

      @redliner Sounds just like the process of how to fix anything on a modern VAG vehicle lol

  • Carsofchaos Bike lanes are in use what maybe 10 to 12 hours a day? The other periods of the day they aren't in use whatsoever. A bike can carry one person and a vehicle can carry multiple people. It's very simple math to figure out that a bike lane in no way shape or form will handle more people than cars will.The bigger issue is double parked delivery vehicles. They are often double parked and taking up lanes because there are cars parked on the curb. You combine that with a bike lane and pedestrians Crossing wherever they feel like it and it's a recipe for disaster. I think if we could just go back to two lanes of traffic things would flow much better. I started coming to the city in 2003 before a lot of these bike lanes were implemented and the traffic is definitely much worse now than it was back then. Sadly at this point I don't really think there is a solution but I can guarantee that congestion pricing will not fix this problem.
  • Charles When I lived in Los Angeles I saw a 9-5 a few times and instanly admired the sweeping low slug aerodynamic jet tech influenced lines and all that beautiful glass. The car was very different from what I expected from a Saab even though the 900 Turbo was nice. A casual lady friend had a Saab Sonnet, never drove or rode in it but nonetheless chilled my enthusiasm and I eventually forgot about Saabs. In the following years I have had seven Mercedes's, three or four Jaguars even two Daimlers both the 250 V-8 and the massive and powerful Majestic Major. Daily drivers of a brand new 300ZX 2+2 and Lincolns, plus a few diesel trucks. Having moved to my big farm in central New York, trucks and SUV's are the standard, even though I have a Mercedes S500 in one of my barns. Due to circumstances with my Ford Explorer and needing a second driver I found the 2006 9-5 locally. Very little surface rust, none undercarriage, original owner, garage kept, wife driver and all the original literature and a ton of paid receipts and history. The car just turned 200,000 miles and I love it. Feels new like I'm back in my Nissan 300ZX with a lot more European class and ready power with the awesome turbo. So fun to drive, the smooth power and torque is incredible! Great price paid to justify going through the car and giving her everything she needs, i.e., new tires, battery, all shocks, struts, control arms, timing chain and rust removable to come, plus more. The problem now is I want to restore it and likely put it in my concrete barn and only drive in good weather. As to the writer, Alex Dykes, I take great exception calling the 9-5 Saab "ugly," finding myself looking back at her beauty and uniqueness. Moreover, I get new looks from others not quite recognizing, like the days out west with my more expensive European cars. There are Saabs eclipsing 300K rourinely and one at a million miles and I believe one car with 500K on the original engine. So clearly, this is a keeper, in love already with my SportCombi. I want to be in that elite club.
  • Marky S. I own the same C.C. XSE Hybrid AWD as in this article, but in Barcelona Red with the black roof. I love my car for its size, packaging, and the fact that it offers both AWD and Hybrid technology together. Visibility is impressive, as is its small turning circle. I consider the C.C. more of a "station wagon" by proportion, rather than an “SUV.” It is fun to drive, with zippy response and perky pick-up. It is a pleasant car to drive and ride in. It is not trying to be a “Butch Off-Roader”, or a cosseting “Luxury Cruiser.” Those are not its goals or purpose. The Corolla Cross XSE Hybrid AWD is a wonderful All-Purpose Car (O.K. – “SUV” if you must hear me say it!) with a combination of all the features it has at a reasonable price.
  • Ernesto Perez There's a line in the movie Armageddon where Bruce Willis says " is this the best idea NASA came up with?". Don't quote me. I'm asking is this the best idea NY came up with? What's next? Charging pedestrians to walk in certain parts of the city? Every year the price for everything gets more expensive and most of the services we pay for gets worse. Obviously more money is not the solution. What we need are better ideas, strategies and inventions. You want to charge drivers in the city - then put tolls on the free bridges like the Brooklyn, Manhattan and Williamsburg bridges. There's always a better way or product. It's just the idiots on top think they know best.
  • Carsofchaos The bike lanes aren't even close to carrying "more than the car lanes replaced". You clearly don't drive in Midtown Manhattan on a daily like I do.